Detergent compositions comprising bleaching enzymes have been described in the prior art. For instance, GB-A-2 101 167 (Unilever) discloses an enzymatic bleach composition in the form of a hydrogen peroxide-generating system comprising C.sub.1 -C.sub.4 alkanol oxidase and a C.sub.1 -C.sub.4 alkanol. Such enzymatic bleach compositions may be used in detergent compositions for fabric washing, in which they may provide a low-temperature enzymatic bleach system. In the wash liquor, the alkanol oxidase enzyme catalyses the reaction between dissolved molecular oxygen and the alkanol to form an aldehyde and hydrogen peroxide. In order to obtain a significant bleach effect at low wash temperatures, e.g. at 15-55.degree. C., the hydrogen peroxide must be activated by means of a bleach activator. Today, the most commonly used bleach activator is tetra-acetyl ethylene diamine (TAED), which yields peracetic acid upon reacting with the hydrogen peroxide, the peracetic acid being the actual bleaching agent.
Although this and several other enzymatic bleach systems have been proposed, there is still a need for alternative or improved enzymatic bleach systems. In particular, the enzymatic bleach system should be capable of bleaching stains which are otherwise difficult to remove, the so-called "problem stains" such as tomato, tea, blackberry juice, or red wine. Such stains would require a significant amount of bleaching for their removal, which might negatively affect the colours of the garment.
In conventional laundry bleach systems, fabrics are uniformly exposed to the same concentration of bleach, whether "problem stains" are present or not. Moreover, repeated washing with conventional bleach systems, which may contain relatively high concentrations of bleach, may cause damage to garments such as the fading of dyes.
It is therefore an object of the present invention to provide alternative or improved enzymatic bleach systems which, in particular, should be capable of bleaching stains which are otherwise difficult to remove, and should preferably be more selective in its bleaching action. It is a further object of the present invention to provide an alternative or improved enzymatic process for bleaching stains on fabrics.
We have now surprisingly found that it is possible to control the bleaching reaction in an enzymatic bleach process by using the bleaching enzyme according to the invention, which is capable of generating a bleaching chemical and has a high binding affinity for non-coloured compounds present in stains on fabrics, said non-coloured compounds having a molecular weight of at least 100, preferably at least 1,000. Even more preferably, the non-coloured compounds have a molecular weight of at least 5,000 and especially preferred are compounds having a molecular weight of at least 10,000. Preferably, the enzyme comprises an enzyme part capable of generating a bleaching chemical, coupled to a reagent having a high binding affinity for the non-coloured compounds present in stains on fabrics.
The new bleaching enzyme is particularly attractive for treating "problem stains" which occur only occasionally, such as fruits and vegetables. These stains are not present on most garments and when they are present they are likely to be present in different positions than habitual stains such as those found on collars and cuffs. According to the invention, it is possible to optimise the in-use concentration of the new bleaching enzyme so that threshold concentrations of bleach are only reached if stain is present and the new bleaching enzyme binds to and accumulates on said stain. When this happens, the high local concentration of enzyme generates a high local concentration of bleach near to the stain and thereby exerts a selective bleaching action where it is required. Therefore, the unstained part of the garment (typically the majority) is not exposed to high levels of bleach and thereby this fabric is protected from bleach-associated damage. Moreover, the next time the same garment has a stain such as fruit or vegetable stains, it is likely to be in a different position on the garment. Therefore, a different position on the garment will be exposed to high levels of bleach. Therefore, problems associated with several washes in conventional bleaching systems, such as dye-fade, will be reduced or eliminated altogether. This is in stark contrast to conventional bleaching systems where all garments are uniformly exposed to high concentrations of bleach, in every wash, regardless of whether problem stains are present or not.